This proposal concerns research in which the muscles of regenerating salamander limbs will be studied to determine the role of neurogenic and myogenic mechanisms in controlling the development of differentiated muscle fiber types. First the properties of normal adult and fully regenerated limb muscle fibers will be determined. Then the sequence of events occurring during normal regenerative development will be established. Subsequently, in order to examine the role of neurogenic and myogenic mechanisms, the effect of denervation and cross-innervation on the sequence of developmental events will be investigated for each fiber type. In this proposed research the enzymatic composition, contractile properties, electrical activity, ultrastructural, and innvervation pattern of muscle fibers will be determined using electrophysiological, histochemical, and electron microscopic techniques. The salamander has been chosen as the experimental animal for this investigation into the mechanisms controlling myogenesis because the embryological tissue of the regenerating limb provides a system that has certain advantages over embryos for the examination of interactions between nerve and muscle tissue during development.